1. Field of the Invention
The present invention generally relates to the fields of tissue engineering, cellular biology, and disease diagnosis. More specifically, the present invention relates to a method and system for measuring single cell mechanics using a scanning probe microscope with a modified probe.
2. Related Art
The responses of living cells to external forces have attracted recent attention in the fields of tissue engineering, cellular biology and cancer research. For example, during the tissue development and wound healing processes, living cells respond to mechanical stimuli in their native environments with biological changes, such as by altering the shape of membranes and nuclei, cell-spreading, actin and microtubule reorganization or cross-linking under cell membrane, or cell bursting/motility. These changes in turn may alter functional synergy as well as the mechanical behavior of cells. On the other hand, it is known that tumor cells exhibit different elastic compliance compared to normal cells. Hence, the ability to directly measure single cell mechanical properties, such as elasticity and Young's modulus, can be extremely useful for characterizing and controlling the mechanical properties and functions of reconstituted tissues in tissue engineering applications, and for identifying diseased cells.
Motivated by the intriguing molecular mechanism of cell response to mechanical forces, and by demand in tissue engineering and other applications, researchers have developed a significant number of techniques and methodologies during the past two decades to facilitate the metrology of cell mechanical properties, and for the understanding of the underlying biological and structural changes. Some more recently developed techniques for measuring cell mechanics include (a) atomic force microscopy (AFM) based imaging and force measurements, and (b) microdevice-based techniques, such as micropipette aspiration, microforce sensors, and cell poker, among others.
Although AFM was developed in 1986 for high-resolution imaging, AFM has also been used to measure forces in the range of 10−5 N-10−11 N. Existing techniques which use an AFM to measure cell mechanics perform local imaging of cell membrane structures and forces at the nanometer scale. However, it is very difficult to accurately quantify the acquired force images of the tip-cell interaction because of lack of knowledge about tip size, geometry, and functionality, as well as lack of a precise mechanic model at the local level.
Microforce devices use optical microscopy as a position guide and can reveal the cell's mechanical behavior under a local or a global mechanical perturbation. However, these techniques require complicated device fabrication techniques. Furthermore, the spatial resolution of those techniques is limited by the optical diffraction limit, and the involvement of complicated models for data analysis (such as finite element analysis) to correlate force distribution with local and whole cell deformation.
The micropipette aspiration technique has been used to study deformation of individual living cells when they are subjected to extracellular pressure. During operation, each cell is drawn into a glass tube with an inner diameter smaller than the cell height through application of aspiration pressure and the cell deformation is monitored using an optical microscope. Unfortunately, this technique has a number of problems: (1) forces are calculated indirectly from cell shape and applied pressure; (2) cell deformation measurements are limited by the diffraction limit; (3) the cell membrane can be ruptured by the micropipette edge; and (4) for each cell size a proper micropipette diameter has to be selected.
Hence, what is needed is a technique for measuring single cell mechanics without the above-described problems.